Prior art target location systems exist, which can identify the latitude, longitude and elevation of a distant target using a laser beam that is directed at the target from an observation point, the latitude, longitude and elevation of which is known. If the latitude, longitude and elevation of an observation point are known, the latitude, longitude and elevation of a point in space that is distant from the observation point can be easily determined using simple trigonometric formulae on the azimuth, elevation angle and distance between the observation point and the target.
Distance to a target point from an observation point can be easily and accurately determined by measuring the time required for a pulse of laser light to traverse the distance between the observation point where a laser is located and the target point. Laser beam elevation angle (positive and negative) and the beam's azimuth angle to a target point are also easily determined. Prior art target location systems that use a laser or other detectable signal are referred to herein as active target location systems.
A problem with prior art active target location systems is that laser light or other electromagnetic energy used to locate or mark a target can be detected. Sighting a target using laser light energy therefore announces to the world that the target is being lased. Using a laser to mark a target and/or determine a target's location therefore has drawbacks. Thus, a need exists for a method and apparatus by which coordinates of a target or other destination point in a three-dimensional space can be determined without having to announce to all those concerned that the target is being marked or lased.